The present invention generally relates to medical devices. More specifically, the present invention relates to medical devices suitable for intravascular ionizing radiation therapy.
Intravascular ionizing radiation therapy is being used increasingly to treat vascular disease. For example, the administration of ionizing radiation has been proposed as both a primary and a secondary therapy for treating vascular stenosis (a vascular restriction or narrowing). Clinical studies have shown that ionizing radiation may be used to inhibit or prevent restenosis after percutaneous transluminal angioplasty (PTA). In coronary applications, such vascular restrictions may range in length from a few millimeters to several centimeters, depending on the extent and nature of the disease, in addition to the size and type of vessel affected.
Typically, physicians evaluate the size and nature of the vascular restriction in order to determine the appropriate treatment parameters (e.g., radiation source length, dose, ect.). Radiation devices commonly utilize a fixed-length ionizing radiation source, and only a limited number of different lengths are available. In some instances, the physician is not able to select a source length that matches the length of the treatment site. In this situation, the physician may elect to use a relatively short radiation source and reposition the source in tandem along the length of the treatment site until the entire site has been exposed to the desired amount of radiation.
However, unless the radiation source is precisely repositioned, various areas of the treatment site will inevitably receive more or less radiation exposure than other areas of the treatment site. Precise repositioning of the radiation source is difficult, if not impossible, due to image foreshortening, even when anatomical landmarks are used as reference points. Thus, there is a need for a more precise method of repositioning the radiation source along the length of the treatment site.
The present invention overcomes these disadvantages by providing a system for intravascular ionizing radiation therapy including a radiation device and a guide wire, wherein the guide wire includes radiopaque markers that facilitate precise repositioning of the radiation device. The radiopaque markers are separated by a distance L, which is equal to the distance between points in the dose fall-off regions (edge effects) corresponding to 50% of the nominal dose. This produces partial dose overlap when the radioactive source is sequentially positioned adjacent each radiopaque marker. Preferably, only the dose fall off regions (edge effects) overlap thereby providing more uniform and complete radiation exposure along the length of the treatment site.
The radiation device may include a centering catheter and a source wire, wherein the source wire is insertable into the centering catheter. The radioactive source is disposed adjacent the distal end of the source wire. The centering catheter preferably includes a guide wire lumen with the guide wire slidably disposed therein. The centering catheter and/or the source wire may include radiopaque markers for alignment with the radiopaque markers on the guide wire.
The radiation source may be a line source having a dosimetry or dose distribution with a nominal dose, a proximal dose fall-off and a distal dose fall-off. The distance L is preferably about equal to the distance between a point in the proximal dose fall-off and a point in the distal dose fall-off. The proximal and distal points preferably correspond to points on the dose distribution equal to half of the nominal dose such that the total dose at the overlap is approximately equal to the nominal dose.
The present invention also provides a method of administering ionizing radiation at a treatment site within a patient""s vasculature. The method includes the steps of: providing a radiation device and a guide wire substantially as described above; navigating the guide wire through the vasculature of the patient until the markers on the guide wire are disposed adjacent the treatment site; inserting the radiation device into the vasculature of the patient over or adjacent to the guide wire; positioning the radioactive source adjacent a marker on the guide wire; and repositioning (in the proximal or distal direction) the radioactive source adjacent the neighboring marker on the guide wire such that slight dose overlap is created thereby providing more uniform and complete radiation exposure along the length of the treatment site.